The invention relates to a process for the preparation of cis-2-tertiary-butylcyclohexanol from 2-tertiary-butylphenol, the cis-isomer being formed under the hydrogenation conditions. 
2-tertiary-butylcyclohexanol, which can arise in the form of the cis and trans stereoisomers, is a valuable intermediate for the preparation of the fragrance 2-tertiary-butylcyclohexyl acetate. In the industrial production of 2-tertiary-butylcyclohexanol, it is desired to obtain large proportions of the cis isomer in order then, by means of transesterification, to obtain cis-2-tertiary-butylcyclohexyl acetate, which is valuable from a perfumery viewpoint and is known under the name Argrumex HC.
For the hydrogenation of 2-tertiary-butylphenol to 2-tertiary-butylcyclohexanol, noble metal catalysts, such as metallic rhodium, rhodium/platinum and rhodium/ruthenium alloys, are known, which are deposited on catalyst supports (JP-A 42-13 938). A disadvantage of the hydrogenation in the presence of a rhodium catalyst is, as well as the high cost of the catalyst, the only low stereoselectivity with regard to the cis-isomer and the decrease in the activity of the catalyst at relatively high temperatures. In addition, tertiary-butylbenzene forms in the rhodium-catalyzed hydrogenation.
DE A 3401343 describes the hydrogenation of 2-tertiary-butylphenol to 2-tertiary-butylcyclohexanol in the presence of palladium and ruthenium, the process being carried out in two stages at hydrogen pressures above 200 bar and temperatures of 70xc2x0-200xc2x0 C. In the first stage, a palladium catalyst is used, and in the second stage, a ruthenium catalyst is used. The cis/trans ratio here is up to 90/10.
JP A 59/065031 describes the hydrogenation of 2-tertiary-butylphenol to 2-tertiary-butylcyclohexanol with Raney cobalt catalysis at 50 bar and 150xc2x0 C., the cis:trans isomer mixture being formed in the ratio 94:6.
DE A 2909663 describes the hydrogenation of 2-tertiary-butylphenol to 2-tertiary-butylcyclohexanol with ruthenium catalysis at 40 bar and 100xc2x0 C., the cis:trans isomer mixture being formed in the ratio 92.5:7.5.
JP A 49/045037 describes the hydrogenation of 2-tertiary-butylphenol to 2-tertiary-butylcyclohexanol with Raney nickel catalysis at 80 bar and 85xc2x0 C. The Raney nickel catalyst is treated prior to use with aqueous sodium boronate solution. Using this catalyst treated in this way, the cis:trans isomer mixture is formed in the ratio 92:8. Without treatment of the Raney nickel catalyst, the cis:trans isomer mixture forms in the ratio 80:20.
A disadvantage of the described prior art is that the service life of the catalyst and the proportion of the cis isomer are inadequate.
Accordingly, it is an object of the present invention to provide a process which produces 2-tertiary-butylcyclohexanol with a high cis isomer content at low cost and guarantees a catalyst service life which is longer than in the prior art.
A process for the preparation of cis-2-tertiary-butylcyclohexanol has been found which is characterized in that 2-tertiary-butylphenol is hydrogenated in the presence of a nickel/iron catalyst mixture and 2-tertiary-butylcyclohexyl acetate.
According to the present invention, preference is given to the use of Raney nickel/iron catalysts. The use of these catalysts in combination with 2-tertiary-butyl-cyclohexyl acetate leads to a 2-tertiary-butylcyclohexanol with a cis/trans isomer mixture of up to 95:5.
By adding 2-tertiary-butylcyclohexyl acetate, the service life of the catalyst can be considerably prolonged. It has been found that the Raney catalyst can be used more than 10 times, if 2-tertiary-butylcyclohexyl acetate is added without the cis:trans ratio falling below 90:10.
Comparative experiments have, on the other hand, shown that without the addition of 2-tertiary-butylcyclohexyl acetate in the hydrogenation, the cis:trans ratio is only 92:8. If the catalyst is used again, the cis:trans ratio decreases even more. When the catalyst is reused for only the third time without the addition of 2-tertiary-butylcyclohexyl acetate, the ratio is only 90:10.
For the process according to the present invention, the catalyst can be used in the dry or moist state.
For the process according to the present invention, in the dry catalyst, the amount of iron is 2-40% by weight, preferably 10-20% by weight; the content of nickel is 60-95% by weight, preferably 70-85% by weight, the content of aluminium is 1-20% by weight, preferably 3-10% by weight.
For the process according to the invention, the weight ratio of the catalyst used to 2-tertiary-butylphenol is (0.0001 to 0.1): 1, preferably (0.01 to 0.03): 1.
The weight ratio of the feed materials 2-tertiary-butylphenol and 2-tertiary-butylcyclohexyl acetate can be 100-0.2:1, preferably 7-9:1.
The reaction temperature for the process according to the invention is 50 to 200xc2x0 C., preferably 90 to 130xc2x0 C.
The hydrogen pressure is 1 to 100 bar, preferably 10 to 20 bar.
The reaction time is 2 to 100 hours, preferably 5 to 20 hours.
The process according to the present invention is generally carried out as follows:
A pressurized container fitted with stirrer is charged with 2-tertiary-butylphenol, 2-tertiary-butylcyclohexyl acetate and the catalyst. Hydrogenation is carried out at the chosen reaction temperature and hydrogen pressure. The resulting cis-2-tertiary-butylcyclohexanol is obtained following removal of the catalyst by filtration, decantation or centrifugation.
The resulting crude mixture can be reacted without further pretreatment with acetic anhydride to give the target product cis-2-tertiary-butylcyclohexyl acetate. Cis-2-tertiary-butylcyclohexyl acetate is a fragrance with woody-fruity properties (S. Steffen Arctander, Perfume and Flavour Chemicals, No. 438, Montclair, N.J., 1969).